This invention relates generally to television systems and networks and more particularly to those cable-television networks and/or wireless television networks in which digital data as well as other information is transmitted through the network, combined with or superimposed on standard television signals so as to make more efficient and economical utilization of available communication channels.
The development and utilization of communication networks such as the Internet has been constrained by the bandwidth limitations of telephone networks. Consequently, the utilization of cable TV networks known as CATV as a means of carrying Internet information has been introduced so as to enable to transmit data as well as video signals of high quality. For example, EP-A-0 742 658, JP-A-04 196792, JP-A-11 041213 and EP-A-0 577 351 disclose various methods for utilizing cable TV for the transmission of additional data. JP-A-04 196792 discloses a CATV subscriber system transmission method utilizing frequency multiplexing between an incoming and an outgoing signal to and from an off premise device. JP-A-11 041213 discloses a conversion circuit converting Internet based data requests to suitable CATV transmission. EP-A-0 577 351 discloses a television signal processing system, the system assigns plural data to the amplitude or phase information in the frequency domain at the transmission side. However, present products enabling Internet users to utilize the advantage of higher-bandwidth CATV are constrained due to the various design limitations of present TV equipment. One of the principal limitations is due to the fact that TV channels were designed to transmit information from a single source to many users. Such a ubiquitous system can hardly allow for the transmission of specific messages intended for review or processing by individuals. The relative bandwidth allowed for applications, other than standard TV transmission, is small compared to the bandwidth reserved for said standard channels, i.e. 30 to 40 Mhz out of 500 to 750 Mhz. One way to overcome this bandwidth limitation and the unilateral nature of TV channels is to combine CATV and additional telephone lines so as to enable the user to send information via the telephone line while receiving information on the cable TV. One example is disclosed in EP-A-0742 658 disclosing a system which considers the multiple channels as one unit and managing such unit via a bandwidth management unit. Another example may be the so-called WebTV system. However, this hybrid solution is forcing the user to connect his terminal both to the TV line as well as to the telephone line, while the “downstream” constraints still exists.
Other ways to use CATV networks for internet applications have been suggested according to which certain channels are dedicated to Internet traffic thereby preventing their simultaneous use for conventional or other television programs, which may reduce the economic effectiveness of the given CATV network.
Furthermore, it is anticipated that in the future, the requirement for bandwidth within interactive networks, enabling users to feed back various queries or data while receiving individual responses through the TV network will increase.
In an effort to overcome constraints inherent to other techniques that have been used for interactive utilization of communication networks such as the Internet in the TV or CATV environments, this invention is proposing methods to send data within the standard TV channels so that facilities already existing for transmission of “downstream” composite TV signals may simultaneously be utilized for carrying additional individual information by superimposing corresponding additional signals on the standard existing TV composite signals without deteriorating the appearance of the video or audio components of said standard TV signals.